Trees just now showing effects of last summer’s drought

Trees in several parts of Washington State are just now showing the damage caused by a stress reaction to dry conditions last summer and this spring. Photo: DNR.

DNR has received many calls from the public in recent weeks about trees whose leaves or needles are turning red or, even, dying.

Glenn Kohler, a DNR forest entomologist, has been investigating and says that Douglas-fir trees between 5 and 15 years old appear to be the ones most affected, but some larger trees are showing symptoms, too. Symptoms include entirely red crowns, red tops and red branches, he says.

“In a typical year, this type of damage may have many causes, but this year it is primarily the result of an extended period with little to no rain during August and September 2012 and a drier-than-normal spring in 2013.”

Most of the trees that Kohler and his colleagues at DNR have examined show no indication of being killed by pathogens, insects, or other animals. Although some trees have been attacked by one of three different species of bark beetles, all signs are that these beetles moved into the trees after they were killed by the dry conditions, Kohler points out.

The damage has been most severe in areas with rocky soils, such as in glacial outwash around the Puget Sound. Fortunately, even in the hardest-hit stands, most trees have had adequate water and are unaffected. Landowners may see an increase in the number of red trees as the weather heats up this summer. If green trees have put out a flush of new expanding bright needles on their branch tips this spring, they are likely to survive, Kohler adds.

Additional information can be found in a report by the Oregon Department of Forestry on the symptoms of water stress injuries to Douglas-fir and other conifers. A longer article on drought effects will be in the next issue of Forest Stewardship Notes, a quarterly publication of DNR and the Washington State University Extension.